Larger Particle Size Means More Flexible and Stronger Cement

In a constant quest for more resilient products, especially dominant products like concrete, material sciences are challenged to create results. HIVE 50 honoree, Rouzbeh Shahsavari, an assistant professor at Rice University, is leading research on innovation in nanoparticle size that can result in stronger and more flexile cement.

Porous particles are important in a host of materials and applications, including drug delivery, insulation, catalysis, chromatography, filler materials, construction materials, and—our favorite—ceramics. But, despite their importance and potential applications, the mechanical properties of such porous particles are often ignored.

Now, after collecting extensive data, researchers at Rice University (Houston, Texas) can definitively say that, when it comes to porous nanoparticles, size matters—and, in the process, they’re made some surprising discoveries about how size affects the materials’ intrinsic properties.

Using uniformly porous calcium-silicate nanoparticles with diameters ranging 150–550 nm and pore sizes of 2–4 nm, the scientists found that larger particles behave differently under pressure than smaller ones. Using a nanoindenter, they tested how assembled films and compacted pellets of the various-diameter nanoparticles held up under pressure.

Rice University materials scientists tested structures made of calcium-silicate nanoparticles and found that particles go from brittle to ductile as they increase in size. The compressed single particle at left deformed under the pressure of a nanoindenter.

The data, the result of more than 900 nanoindentation experiments, shows that self-assembled films of larger calcium-silicate nanoparticles are 120% tougher than those assembled from smaller particles of the same composition and porousness.

“This means that larger submicron calcium-silicate particles are tougher and more flexible compared with smaller ones, making them more damage-tolerant,” senior researcher Rouzbeh Shahsavari says in a Rice University news release.

Rouzbeh completed the study with graduate student Sung Hoon Hwang, who together also recently wrote an interesting article about innovative concretes in the most recent January/February 2018 issue of the ACerS Bulletin.

But hold up—when contemplating particle size, wouldn’t you expect that a material made up of smaller particles would actually be more ductile than one with a larger nanoparticle composition?

“Usually the common perception in nanomaterials is that smaller is better (such as in metallic systems), but our results were the opposite,” Shahsavari explains in an email. “This new knowledge can help to better create and use either individual version of these particles, for example for drug delivery—or their collected behavior, such as in self-healing applications and bone-tissue engineering.”